1. Field of the Invention
The present invention relates to a valve timing adjusting device that controls opening and closing timing of an intake valve or an exhaust valve of an internal combustion engine such as a motor engine (hereinafter referred to as an “engine”).
2. Description of the Related Art
A conventional valve timing adjusting device is generally composed of a first rotor that is connected to a crankshaft of an engine by a rotational-driving force-transmitting member such as a chain, and that rotates synchronously with the crankshaft; a second rotor that is relatively rotatably by a predetermined angle provided within the first rotor, and is integrally secured on the end face of an intake camshaft or an exhaust camshaft of the engine; and a plurality of oil-pressure chambers partitioned between the second rotor and the above first rotor. The device is arranged such that hydraulic pressure of an oil pump, which takes a charge of supplying oil to a sliding portion of the engine, is applied to and exhausted from these oil-pressure chambers, and that the hydraulic pressure controls a relative position of the second rotor with respect to the first rotor.
In such valve timing adjusting devices, there are some valve timing adjusting devices equipped with a locking mechanism that restricts a relative rotation between the first rotor and the second rotor at the initial position in order to prevent the first rotor and the second rotor from accidentally contacting with each other and from thereby producing abnormal noises at the time of an engine start where oil-pressure is still low. This locking mechanism is generally composed of a lock hole formed in the one rotor and a lock pin provided engageably in the other rotor within the lock hole. In addition, there are some valve adjusting devices disclosed in JP 2002-295210 A and JP 2002-276312 A which includes an assisting spring placed in the oil-pressure chamber for urging, e.g., the second rotor to the advanced side of the first rotor rotates in the direction of rotation even when hydraulic pressure in the oil-pressure chamber is low, out of necessity of quickly rotating and returning the second rotor to the initial position with respect to the first rotor. As the conventional assisting spring, a compression spring is used. For example, JP 11-325309 A discloses an assisting spring of this kind.
However, when the second rotor is relatively rotates with respect to the first rotor (e.g., to the lagged side), seats of both the ends of the compression spring are restrained from being maintained in parallel at the time of expansion of the spring. For this reason, the compression spring is bent, and the spring may come in contact with an inner peripheral surface, with the result that the spring may not acquit its function as the assisting spring. Further, when the valve timing adjusting device with such a compression spring has a wide rotation angle, the spring is liable to bent. Therefore, it is difficult to set a wider rotation angle. As a remedy for conquering this difficulty, it is imaginable providing a mechanism for guiding the compression spring in a straight line to prevent the compression spring from being excessively bent. However, the guiding mechanism is effective only for hindering the compression spring from being excessively bent, the mechanism forces the compression spring to be maintained in a straight line. Therefore, the mechanism inherently involves incommodities that the compression spring strains a large load, and the spring suffers from reduced durability.